Some recent findings on climate change:
globalwarming.org
Science
NRC Report Clarification
The recent National Research Council report on the discrepancy between the surface-based and satellite-based temperature records received a lot of press attention. Most of it was wrong, according to John M. Wallace, chairman of the panel, and John R. Christy, a member of the panel. "When the report hit the streets, several news outlets across the country cited it as one more piece of definitive evidence that greenhouse gases were causing the Earth to warm," they said. "Policy makers rushed to announce initiatives to combat the problem."
Wallace and Christy chastise those who try to turn global warming into a "pro" or "con" issue. "To really understand long-term global climate change, we have to pay attention to what the science tells us," they said. "And like it or not, the evidence to date is telling us that while we?re making great strides, we still don?t have all the answers."
Wallace and Christy conclude, "Despite differences in the two sets of temperature data, the Earth?s surface is in fact warming. Our panel did not address whether greenhouse gases have led to the temperature increases of the past two decades.
Unfortunately, the important distinction between greenhouse warming and global warming was all but ignored by some policy makers and interest groups who seized on our findings to further their own agendas. Many scientists do believe that increasing greenhouse gases or other human-induced changes are responsible for the warming, but some still have reasonable doubts" (HMS Beagle, www.biomednet.com/hmsbeagle, February 18, 2000).
Tropospheric Temperature Change
With the release of the NRC report, there has been a lot of discussion about the discrepancy in temperature trends as measured on the surface and in the layer of the atmosphere known as the troposphere. Two new papers in Science (February 18, 2000) address the issue. Both papers confirm the accuracy of the satellite temperature data.
One is a paper that discusses the use of balloon borne radiosonde temperature measurements as confirmation of the satellite data. The lead author is Dian Gaffen of the Air Resources Laboratory, NOAA, and is co-authored by John Christy of Earth System Science Laboratory, University of Alabama-Huntsville, among others. Gaffen et al. offers possible explanations of the temperature discrepancy, such as "Surface and lower tropospheric temperatures may respond differently to changes in a suite of natural and human-induced climate forcings, including well-mixed greenhouse gases, stratospheric and tropospheric ozone, tropospheric aerosols, and stratospheric volcanic aerosols."
The discrepancy is largest at the tropical belt and so the paper focuses on the temperature trends for those areas. Balloon measurements of the tropical belt began in 1960 and show that the lower to mid troposphere actually warmed faster than the surface in "a pattern consistent with model projections of the vertical structure of tropospheric warming associated with increasing concentrations of well-mixed atmospheric greenhouse gases. From 1979 to 1997, however, the balloon data "show the same pattern of surface warming and tropospheric cooling since 1979 as the independent surface and MSU (satellite) observations."
Another confirmation of the satellite data is observed changes in the tropical freezing level, which is closely correlated with tropospheric temperatures. From 1960 to 1997, the freezing level rose by about 30 meters per decade, but during the period of satellite measurements since 1979 the freezing level has fallen. Interestingly, "Tropical glaciers at the 5- to 7-km elevation have retreated during the 1980s and 1990s, while freezing levels have lowered."
A paper by Ben Santer of Lawrence Livermore National Laboratory and Tom Wigley of the National Center for Atmospheric Research, among others (including Gaffen), analyzed three state-of-the-art climate models to see how well they could account for the discrepancy. Gaffen, et al., noted that the analysis, "suggests that simulated global surface temperature trends over 20-year periods never exceed lower tropospheric trends by as much as" that observed during the 1979 to 1998 period. Even when "forced" by changes in atmospheric concentrations of greenhouse gases, sulfate aerosols, stratospheric ozone depletion and the Mount Pinatubo eruption, the models failed to simulate the trend differences. Santer et al. also argues that part of the discrepancy is due to incomplete surface temperature records.
Gaffen et al. concludes that, "Given uncertainties in the observations, in reconstructing the historical climate forcings, and in the climate system?s response to those forcings, we may never have a complete understanding of the complex behavior of tropical tropospheric temperatures, lapse rates, and freezing levels during the past few decades."
What is the implication of these papers? Dr. Christy told MSNBC (February 18, 2000) that, "The behavior of the surface temperatures and the atmosphere over the past 21 years is at odds with the theories that explain how human-induced climate changes should occur. This suggests that what has happened in the past 21 years is not an example of human-induced climate change."
Climate Model Uncertainties
Computer models are being used with increased frequency to evaluate and solve problems, writes Barry Cipra in an article in Science (February 11, 2000). These models can be useful, but they also have their drawbacks.
"Although the precise numbers and realistic pictures produced by computer simulations give an illusion of accuracy," says Cipra, "a ravening swarm of assumptions, simplifications, and outright errors lurk beneath." Better tools are needed, but according to Cipra, "The quest for such tools is itself an uncertain and challenging process."
Take global warming, for instance. "Much of the global warming debate," says Cipra, "is fueled by the radically different numbers that different models produce. As the explosive growth of computer power allows researchers to tackle ever-bigger problems with ever-more-complex models, even the experts have a hard time sorting the scientific wheat from the numerical chaff."
Mac Hyman, a mathematician at Los Alamos National Laboratory, says that the number of variables and size of the system being analyzed is so great that even the fastest computers strain under the computational requirements.
A Five Century Temperature Trend
Nature (February 17, 2000) has published a paper showing that the Earth has warmed gradually over the last 500 years. By measuring the temperature in boreholes (deep holes in the ground) "at 10-m depth intervals to depths as great as 600 m," the researchers found a long term global warming. They also found that, "Almost 80% of the net temperature increase observed has occurred in the nineteenth and twentieth centuries."
Of course, prior to the nineteenth and twentieth centuries, the Earth was in the depths of the Little Ice Age. The end of the Little Ice Age was only 100 to 150 years ago, so these findings are not particularly surprising.
Research Group: Polar Ice Sheets to Remain Stable
The Cooperative Research Center for Antarctica and the Southern Ocean (Antarctic CRC) released a position statement on February 10 entitled "Polar Ice Sheets, Climate and Sea-Level Rise." The statement?s findings are part of Antarctic CRC?s contribution to the Intergovernmental Panel on Climate Change.
According to the statement, "There is popular speculation that greenhouse warming of two or three degrees over the next century might trigger a similarly large change in association with melting of the two remaining ice-sheets of Greenland and Antarctica." A few degrees warming, says the statement, may melt most of the Greenland ice-sheet, raising sea levels by six meters, but that would take 1,000 to 2,000 years.
The Antarctic ice-sheet, if completely melted, would raise sea levels by 55 meters but, "It is not expected that it would melt as a result of a warming of two or three degrees. This is because temperatures in most of the Antarctica are well below the melting point of ice." At most, increased ice flows from the Antarctic ice-sheet due to warming would increase the sea level by one or two meters over the next 1,000 to 2,000 years.
The statement concludes, "In the shorter term ? that is, over the next century or two ? it is expected that there will be relatively little melting of the ice-sheets. Indeed it is expected that the volume of Antarctic ice will increase slightly because greater snowfall caused by higher evaporation from the warmer oceans will outweigh any increase in melting."
The highest predicted sea level increase is "several tens of centimeters per century," according to the statement. "This is good news," said Professor Garth Paltridge, the institute?s director. The statement can be found by clicking "News Flash" at www.antcrc.utas.edu.au/antcrc.
|
